The present invention generally relates to the injection of contrast medium during vascular therapy and more particularly pertains to improved devices and methods for more efficiently and effectively delivering radiopaque dye to a treatment site.
During vascular therapy such as an angioplasty procedure or the stenting of a diseased area, it is highly desirable to be able to inject a contrast medium such as a radiopaque dye into the vessel upstream of the diseased site in order to check the flow past the site. This enables the physician to precisely locate the stenosis and assist in properly positioning the treatment device prior to treatment. After treatment, the injection of dye allows a determination to be made as to whether the procedure was successful or whether further treatment of the site, manipulation of the stent, or some other procedure is necessary.
A number of different techniques have previously been employed to deliver contrast medium to a treatment site. In one such method, contrast medium is injected via the guide or guiding catheter and more particularly through the annulus defined by the interior surface of the guide catheter and the exterior surface of the treating catheter extending therethrough. A number of shortcomings are, however, inherent in such approach. Because the guide catheter is relatively large and stiff, its access to smaller arteries and typically those being treated, is precluded. In the treatment of a coronary artery, for example, the guide catheter can be advanced no further than into the aortic root adjacent the mouth of the artery being treated. The treatment catheter must then extend therefrom into the treatment artery and on to the treatment site. As a consequence, in order to cause dye at a concentration sufficiently high to create a satisfactory image to be flushed past the treatment site, it is necessary to inject a relatively large quantity of the contrast medium. The quantity of dye must be sufficient to fill not only the entire volume of the treatment vessel proximal to the treatment site but must additionally compensate for the significant quantity that can be expected to leak into the aorta as no positive seal is formed between the distal end of the guide catheter and the entrance to the treatment vessel. Moreover, such quantity may have to be injected at multiple times or continuously for extended periods of time. Introduction of such large quantities may, however, be detrimental. Introduction of such large quantities may, however, be detrimental to tissue downstream of the injection site, in particular, brain tissue distal to a diseased carotid artery because it has the potential to displace oxygen carrying blood. Large contrast dye injections can also cause renal failure because the kidneys must process the additional fluid and restore the osmotic balance in the body. Delivery of the large quantity of dye that is needed for such a method is further complicated by the fact that the cross-sectional area of the annulus through which it is forced along the entire length of the catheter is rather small. As a result, injection under high pressure is needed to overcome the restricted flow.
An alternative to the use of the guide catheter to deliver contrast medium is the use of the guide wire lumen that is formed in the delivery catheter. After a standard over-the-wire design balloon catheter or stent deployment catheter is advanced to the treatment site, the guide wire can be removed and the catheter lumen used as a conduit for injection. This minimizes the amount of dye that is needed to generate an image of the treatment site and obviates the possibility of leakage into the aorta thus precluding the distribution of dye to other parts of the body. The principal disadvantage inherent in the use of such technique is that the guide wire must be removed. Because the guide wire must be replaced before another device can be inserted, in case of an emergency, such as a dislodged embolic particle, vessel spasm, or abrupt vessel closure, additional therapeutic devices cannot be placed quickly. For example, should plaque become dislodged by the injection, the stent would not yet be in position for expansion. Additionally, should such technique be used in conjunction with the delivery of a balloon expandable stent, the treatment catheter must be retracted for each viewing of the site. Each such shifting of the catheter within the artery increases the risk of dislodging plaque which upon being swept downstream and into the smaller arteries thereby embolizing and may even cause thrombosis. Moreover, attempting to precisely reposition the catheter in the treatment site after each injection may be difficult to achieve as well as time consuming.
A device and associated method is needed that minimizes the amount of dye that must be injected into the vasculature in order to provide a good visualization of the treatment site and obviates the need to shift any device within the artery in order to inject the dye.